An illegal occupancy could result in your eviction, and it sounds like this may such a situation. As if the unit was truly a duplex and separate rental, then you should have your own mailbox! You may wish to seek a separate mailing address at a PO Box, if you still want to stay in the residence. Or address the issue head on with the Landlord, or housing authorities, but again that may result in an eviction, or possible termination of lease/residency as well! I truly wish you the best of luck! As an aside, if you found my direction helpful, and if you feel appropriate; could you be so kind as to designate my answer as the “best” answer to your question?